There is a much easier way of accomplishing this effect than Derren suggests. You simply exchange the paper with a wish on it!Instead of complicated psychological manipulation, he probably used some sleight of hand and his pickpocketing skills. He replaced the real wish (BMX bike) with a fake wish (a leather jacket). I am sure it is easier to fake someone's handwriting than to mess with his memory.Which explanation do you find more plausible? It is up to you to decide.